[Show abstract][Hide abstract] ABSTRACT: A first direct intercomparison of aerosol vertical profiles from Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations, performed during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI) in summer 2009, is presented. Five out of 14 participants of the CINDI campaign reported aerosol extinction profiles and aerosol optical thickness (AOT) as deduced from observations of differential slant column densities of the oxygen collision complex (O4) at different elevation angles. Aerosol vertical profiles and AOT are compared to backscatter profiles from a ceilometer instrument and to sun photometer measurements, respectively. Furthermore, the near-surface aerosol extinction coefficient is compared to in-situ measurements of a humidity controlled nephelometer and dry aerosol absorption measurements. The participants of this intercomparison exercise use different approaches for the retrieval of aerosol information, including the retrieval of the full vertical profile using optimal estimation and a parametrised approach with a prescribed profile shape. Despite these large conceptual differences, and also differences in the wavelength of the observed O4 absorption band, good agreement in terms of the vertical structure of aerosols within the boundary layer is achieved between the aerosol extinction profiles retrieved by the different groups and the backscatter profiles observed by the ceilometer instrument. AOT from MAX-DOAS and sun photometer show a good correlation (R > 0.8), but all participants systematically underestimate the AOT. Substantial differences between the near-surface aerosol extinction from MAX-DOAS and from the humidified nephelometer remain largely unresolved.
[Show abstract][Hide abstract] ABSTRACT: SKYNET and AERONET retrieved aerosol single scattering albedo (SSA) values of four sites, Chiba (Japan), Pune (India), Valencia (Spain), and Seoul (Korea), were compared to understand the factors behind often noted large SSA differences between them. SKYNET and AERONET algorithms are found to produce nearly same SSAs for similarity in input data, suggesting that SSA differences between them are primarily due to quality of input data due to different calibration and/or observation protocols as well as difference in quality assurance criteria. The most plausible reason for high SSAs in SKYNET is found to be underestimated calibration constant for sky radiance (△Ω). The disk scan method (scan area: 1°x1° area of solar disk) of SKYNET is noted to produce stable wavelength dependent △Ω values in comparison to those determined from the integrating sphere used by AERONET to calibrate sky radiance. Aerosol optical thickness (AOT) difference between them can be the next important factor for their SSA difference, if AOTs between them are not consistent. Inconsistent values of surface albedo while analyzing data of SKYNET and AERONET can also bring SSA difference between them, but the effect of surface albedo is secondary. The aerosol non-sphericity effect is found to be less important for SSA difference between these two networks.
Full-text · Article · Jan 2016 · Journal of Geophysical Research Atmospheres
[Show abstract][Hide abstract] ABSTRACT: An investigation into the diurnal characteristics of vertical formaldehyde (HCHO) profiles was conducted based on multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Beijing during the CAREBEIJING campaign, covering a month-long period through August and September 2006. Vertical HCHO profiles were retrieved based on a combined differential optical absorption spectroscopy (DOAS) technique and an optimal estimation method (OEM). The HCHO volume-mixing ratio (VMR) was found to be highest in the layer from the surface up to an altitude of 1 km and to decrease with altitude above this layer. In all retrieved profiles, HCHO was not detected in the layer from 3-4 km. Over the diurnal cycle, the HCHO VMR values were generally highest at 15:00 local time (LT) and were lower in the morning and late afternoon. The mean HCHO VMRs were 6.17, 1.82, and 0.80 ppbv for the 0-1, 1-2, and 2-3-km layers, respectively, at 15:00 LT, whereas they were 3.54 (4.79), 1.06 (1.43), and 0.46 (0.63) ppbv for the 0-1, 1-2, and 2-3-km layers, respectively, at 09:00 (17:00) LT. The HCHO VMRs reached their highest values at 15:00 LT on August 19, which were 17.71, 5.20, and 2.31 ppbv for the 0-1, 1-2, and 2-3-km layers, respectively. This diurnal pattern implies that the photo-oxidation of volatile organic compounds (VOCs) was most active at 15:00 LT for several days during the campaign period. In a comparison of the derived HCHO VCDs with those obtained from the Ozone Monitoring Instrument (OMI) measurements, the HCHO vertical column density (VCD) values obtained from the OMI measurements tend to be smaller than those from the MAX-DOAS.
[Show abstract][Hide abstract] ABSTRACT: Distributions and optical characteristics of aerosols were continuously observed with a polarization- sensitive (532 nm), Mie-scattering (532 and 1064 nm) and Raman-scattering (607 nm) lidar and a sky radiometer in Phimai, Thailand. Polarization lidar measurements indicated that high concentration plumes of spherical aerosols considered as biomass burning smoke were often observed in the dry season. Plumes of non-spherical aerosols considered as long-range transported soil dust from Africa, the Middle East, or Northeast Asia were occasionally observed. Furthermore, low-concentration non- spherical aerosols were almost always observed in the atmospheric mixing layer. Extinction coefficient profiles of spherical aerosols and non-spherical dust exhibited different diurnal variations, and spherical aerosols including smoke were distributed in higher altitudes in the mixing layer and residual layer. The difference can be explained by hygroscopic growth of smoke particles and buoyancy of the smoke. Analysis of seasonal variations of optical properties derived from the Raman lidar and the sky radiometer confirmed that the lidar ratio, aerosol optical depth, and Angstrom exponent were higher in the dry season (October–May) and lower in the wet season (June–September). The single scattering albedo was lower in the dry season. These seasonal variations are explained by frequent biomass burning in the dry season consistent with previous studies in Southeast Asian region. At the same time, the present work confirmed that soil dust was a major aerosol component in Phimai, Thailand.
Full-text · Article · Jun 2015 · Environmental Research Letters
[Show abstract][Hide abstract] ABSTRACT: Continuous NO2 profile observations have been made using ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) at Fukuoka (33.55°N, 130.36°E), an urban area in Japan. Throughout the year, NO2 variations measured by MAX-DOAS (0–100 m) are in good agreement with in situ surface NO2 measurements on several-day, week-to-week, and seasonal timescales. We investigated the spatiotemporal inhomogeneity in NO2 over Fukuoka by observing at two azimuth angles: the Tenjin (towards the city center) and Itoshima (away from the city center) directions. In terms of diurnal variations, NO2 in both directions show clear morning maxima, on account of local emissions in the morning and the development of a boundary layer. The concentrations in the early morning are nearly the same in both directions, but they are higher in the Tenjin direction during most of the daytime on average. Variability in both directions, as well as spatial inhomogeneity, is large during most of the daytime except for in the morning. The diurnal maximum for 0–1 km between 10 and 13 LT is sometimes observed in the Tenjin direction; in some cases, 1 h after this maximum, a maximum is also observed in the Itoshima direction. The NO2 maxima for the upper level (1–2 km) in both directions are also delayed from the maximum in the Tenjin direction for 0–1 km. Analysis of the surface wind field indicates that the NO2 inhomogeneity is strongly related to vertical/horizontal transport of high concentrations of NO2 from the city center, and to horizontal transport of low concentrations from the ocean via a land–sea breeze. Three-dimensional continuous observations by MAX-DOAS are potentially a powerful tool for increasing our understanding of pollutant transport and mixing in urban areas.
No preview · Article · Jan 2015 · Atmospheric Environment
[Show abstract][Hide abstract] ABSTRACT: Coincident aerosol observations of Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS), Cavity Ring Down Spectroscopy (CRDS), lidar, and sky radiometer were conducted in Tsukuba, Japan on 5–18 October 2010. MAX-DOAS aerosol retrieval (for aerosol extinction coefficient and aerosol optical depth at 476 nm) was evaluated from the viewpoint of the need for a correction factor for oxygen collision complexes (O4 or O2-O2) absorption. The present study strongly supports this need, as systematic residuals at relatively high elevation angles (20 and 30°) were evident in MAX-DOAS profile retrievals conducted without the correction. However, adopting a single number for the correction factor (fO4 = 1.25) for all of the elevation angles led to systematic overestimation of near-surface aerosol extinction coefficients, as reported in the literature. To achieve agreement with all three observations, we limited the set of elevation angles to ≤ 10° and adopted an elevation-angle-dependent correction factor for practical profile retrievals with scattered light observations by a ground-based MAX-DOAS. With these modifications, we expect to minimize the possible effects of temperature-dependent O4 absorption cross section and uncertainty in DOAS fit on an aerosol profile retrieval, although more efforts are encouraged to quantitatively identify a physical explanation for the need of a correction factor.
[Show abstract][Hide abstract] ABSTRACT: We assess the standard operational nitrogen dioxide (NO2) data product (OMNO2, version 2.1) retrieved from the Ozone Monitoring Instrument (OMI) onboard NASA's Aura satellite using a combination of aircraft and surface in~situ measurements as well as ground-based column measurements at several locations and a bottom-up NOx emission inventory over the continental US. Despite considerable sampling differences, NO2 vertical column densities from OMI are modestly correlated (r = 0.3–0.8) with in situ measurements of tropospheric NO2 from aircraft, ground-based observations of NO2 columns from MAX-DOAS and Pandora instruments, in situ surface NO2 measurements from photolytic converter instruments, and a bottom-up NOx emission inventory. Overall, OMI retrievals tend to be lower in urban regions and higher in remote areas, but generally agree with other measurements to within ± 20%. No consistent seasonal bias is evident. Contrasting results between different data sets reveal complexities behind NO2 validation. Since validation data sets are scarce and are limited in space and time, validation of the global product is still limited in scope by spatial and temporal coverage and retrieval conditions. Monthly mean vertical NO2 profile shapes from the Global Modeling Initiative (GMI) chemistry-transport model (CTM) used in the OMI retrievals are highly consistent with in situ aircraft measurements, but these measured profiles exhibit considerable day-to-day variation, affecting the retrieved daily NO2 columns by up to 40%. This assessment of OMI tropospheric NO2 columns, together with the comparison of OMI-retrieved and model-simulated NO2 columns, could offer diagnostic evaluation of the model.
Full-text · Article · Nov 2014 · Atmospheric Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: Total and tropospheric NO 2 columns have been operationally retrieved from the GOME-2/MetOp instruments since the first MetOp platform was put in orbit in October 2006. GOME-2 NO 2 data products are retrieved in three main steps: (1) a DOAS spectral analysis yielding the total column amount of NO 2 along the slant optical path, (2) an estimation of the stratospheric NO 2 column using tropospheric masking and spatial interpolation, to be subtracted from the total column to derive the tropospheric contribution, and (3) a conversion of the total and tropospheric slant columns into vertical columns based on airmass factor calculations which require a-priori knowledge of the NO 2 vertical distribution and surface albedo, as well as cloud information retrieved from GOME-2 spectra. In this study we combine correlative measurements available from complementary ground-based remote sensing networks to address the geophysical validation of the GOME-2 NO 2 data products. Zenith-sky DOAS/SAOZ measurements at the usually unpolluted stations of the NDACC network are used to validate the stratospheric NO 2 columns retrieved from the satellite, while direct-sun Pandora and multi-axis MAXDOAS data sets from a number of stations of the NDACC and MADRAS networks are used to investigate the consistency of GOME-2 total and tropospheric NO 2 columns in urban, sub-urban and background conditions. Results are discussed in terms of observed biases between satellite and ground-based data sets, their dependence on location, season and cloud conditions, and for the stratospheric columns, their photochemical effects.
[Show abstract][Hide abstract] ABSTRACT: We conducted long-term network observations using standardized Multi-Axis Differential optical absorption spectroscopy (MAX-DOAS) instruments in Russia and ASia (MADRAS) from 2007 onwards and made the first synthetic data analysis. At seven locations (Cape Hedo, Fukue and Yokosuka in Japan, Hefei in China, Gwangju in Korea, and Tomsk and Zvenigorod in Russia) with different levels of pollution, we obtained 80 927 retrievals of tropospheric NO2 vertical column density (TropoNO2VCD) and aerosol optical depth (AOD). In the technique, the optimal estimation of the TropoNO2VCD and its profile was performed using aerosol information derived from O4 absorbances simultaneously observed at 460-490 nm. This large data set was used to analyze NO2 climatology systematically, including temporal variations from the seasonal to the diurnal scale. The results were compared with Ozone Monitoring Instrument (OMI) satellite observations and global model simulations. Two NO2 retrievals of OMI satellite data (NASA ver. 2.1 and Dutch OMI NO2 (DOMINO) ver. 2.0) generally showed close correlations with those derived from MAX-DOAS observations, but had low biases of up to ∼50%. The bias was distinct when NO2 was abundantly present near the surface and when the AOD was high, suggesting a possibility of incomplete accounting of NO2 near the surface under relatively high aerosol conditions for the satellite observations. Except for constant biases, the satellite observations showed nearly perfect seasonal agreement with MAX-DOAS observations, suggesting that the analysis of seasonal features of the satellite data were robust. Weekend reduction in the TropoNO2VCD found at Yokosuka and Gwangju was absent at Hefei, implying that the major sources had different weekly variation patterns. While the TropoNO2VCD generally decreased during the midday hours, it increased exceptionally at urban/suburban locations (Yokosuka, Gwangju, and Hefei) during winter. A global chemical transport model, MIROC-ESM-CHEM (Model for Interdisciplinary Research on Climate-Earth System Model-Chemistry), was validated for the first time with respect to background NO2 column densities during summer at Cape Hedo and Fukue in the clean marine atmosphere.
[Show abstract][Hide abstract] ABSTRACT: Satellite observations of the tropospheric NO2 vertical column density (VCD) are closely correlated to, and thus can be used to estimate, surface NOx emissions. In this study, the NO2 VCD simulated by a regional chemical transport model with emissions data from the updated Regional Emission inventory in ASia (REAS) version 2.1 were validated through comparison with multisatellite observations during the period 2000–2010. Rapid growth in NO2 VCD (~11% year−1) driven by the expansion of anthropogenic NOx emissions was identified above the central eastern China (CEC) region, except for the period during the economic downturn. In contrast, slightly decreasing trends (~2% year−1) were identified above Japan accompanied by a decline in anthropogenic emissions. To systematically compare the modeled NO2 VCD, we estimated sampling bias and the effect of applying the averaging kernel information, with particular focus on the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) data. Using the updated REAS, the modeled NO2 VCD reasonably reproduced annual trends observed by multisatellites, suggesting that the rate of increase of NOx emissions estimated by the updated REAS inventory would be robust. Province-scale revision of emissions above CEC is needed to further refine emission inventories. Based on the close linear relationship between modeled and observed NO2 VCD and anthropogenic NOx emissions, NOx emissions in 2009 and 2010, which were not covered by the updated REAS inventory, were estimated. NOx emissions from anthropogenic sources in China in 2009 and 2010 were determined to be 26.4 and 28.5 Tg year−1, respectively, indicating that NOx emissions increased more than twofold between 2000 and 2010. This increase reflected the strong growth of anthropogenic emissions in China following the rapid recovery from the economic downturn from late 2008 until mid-2009. Our method consists of simple estimations from satellite observations and provides results that are consistent with the most recent inventory of emissions data for China.
[Show abstract][Hide abstract] ABSTRACT: Unlabelled:
NO2 vertical column densities (VCDs) over East Asia in June and December 2007 were simulated by the Community Multi-scale Air Quality (CMAQ) version 4.7.1 using an updated and more elaborate version of the Regional Emission Inventory in Asia (REAS) version 2. The modeling system could reasonably capture observed spatiotemporal changes of NO2 VCDs by satellite sensors, the Global Ozone Monitoring Experiment-2 (GOME-2), the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY), and the Ozone Monitoring Instrument (OMI), even at the coarsest horizontal resolution of 80 km. The CMAQ simulations were performed in a sequence of three horizontal resolutions (80 km, 40 km, and 20 km) for June and December 2007 to investigate the influence of changes of horizontal resolution on the obtained NO2 VCDs. CMAQ-simulated NO2 VCDs generally increased with improvements in resolution from 80 km to 40 km and then to 20 km. Increases in the CMAQ-simulated NO2 VCDs were greater for the change from 80 km to 40 km than for those from 40 km and 20 km, in which the increases of NO2 VCDs due to the improvement of horizontal resolution were approached convergence at the horizontal resolution of approximately 20 km. Conversely, no clear convergences in NO2 VCDs changes were found at near Tokyo and over the East China Sea. The biases of the NO2 VCDs simulated at a resolution of 20 km against the satellite retrievals were -36% near Beijing (CHN1) and -78% near Shanghai (CHN2) in summer; these errors were found to be comparable to the horizontal resolution-dependent errors, which were 18-25% at CHN1 and 44-58% at CHN2 from 80 km to 40 km. Conversely, the influence of changes of horizontal resolution in winter was relatively less compared to that in summer.
NO2 VCDs over East Asia in June and December 2007 were simulated using CMAQ version 4.7.1 and REAS version 2. The modeling system could reasonably capture observed spatiotemporal changes of NO2 VCDs by satellite sensors. The CMAQ simulations were performed in a sequence of three horizontal resolutions, 80, 40, and 20 km, to investigate the influence of changes of horizontal resolution on the obtained NO2 VCDs. The results suggested that the influence of changes of horizontal resolution was larger in summer compared to that in winter. The magnitude of the influence was comparable to the biases of the NO2 VCDs simulated at a resolution of 20 km against the satellite retrievals.
Preview · Article · Apr 2014 · Journal of the Air & Waste Management Association (1995)
[Show abstract][Hide abstract] ABSTRACT: We investigated the effect of surface reflectance anisotropy, Bidirectional Reflectance Distribution Function (BRDF), on satellite retrievals of tropospheric NO2. We assume the geometry of geostationary measurements over Tokyo, which is one of the worst air-polluted regions in the East Asia. We calculated air mass factors (AMF) and box AMFs (BAMF) for tropospheric NO2 to evaluate the effect of BRDF by using the radiative transfer model SCIATRAN. To model the BRDF effect, we utilized the Moderate Resolution Imaging Spectroradiometer (MODIS) products (MOD43B1 and MOD43B2), which provide three coefficients to express the RossThick-LiSparseReciprocal model, a semi-empirical and kernel-based model of BRDF. Because BRDF depends on the land cover type, we also utilized the High Resolution Land-Use and Land-Cover Map by the Advanced Land Observing Satellite (ALOS)/Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2), which classifies the ground pixels over Tokyo into six main types: water, urban, paddy, crop, deciduous forest and evergreen forest. We first develop an empirical model of the three BRDF coefficients for each land cover type over Tokyo, and then apply the model to the calculation of land cover type dependent AMFs and BAMFs. Results show that the variability of AMF among the land types is up to several tens percent, and if we neglect the reflectance anisotropy, the difference from BRDF's AMF reaches 10% or more. The evaluation of the BAMFs calculated shows that not to consider variations in BRDF will cause large errors if the concentration of NO2 is high close to the surface, although the importance of BRDF for AMFs decreases for large aerosol optical depth (AOD).
Preview · Article · Mar 2014 · Atmospheric Measurement Techniques
[Show abstract][Hide abstract] ABSTRACT: Differential optical absorption spectroscopy (DOAS) is a useful technique for measuring nitrogen dioxide (NO2) and aerosol, the most important species in urban environmental pollution. This paper reports on the results of our dual path DOAS measurements recently conducted in Chiba City, Japan, using xenon flashlights equipped on tall constructions as aviation obstruction lights. Because of the proximity of the southern DOAS path to an industrial area, it is found that the level of air pollution generally increases with the dominance of westerly winds, from the plausible source area to the observation light path. This situation is consistent with the result of wind lidar measurement covering a sector of ±28? with the observation range of approximately 2.8 km. In spite of the fact that the two DOAS paths, having path lengths of 5.5 and 3.5 km each, are located in separated regions of Chiba City, the observed temporal behavior was similar for both nitrogen dioxide and aerosol, though the southern path tends to exhibit slightly higher pollution levels than the northern counterpart. Additionally it is confirmed that size information of aerosol particles can be derived from the DOAS data through the analysis of the wavelength dependence of the aerosol optical thickness, which shows fairly good correlation with the mass ratio between PM2.5 and suspended particulate matter (SPM) obtained from the in-situ sampling station measurement. Thus, the DOAS approach can also be utilized for obtaining information on PM2.5 that is considered to be more harmful to human health than SPM.
No preview · Article · Mar 2014 · Open Journal of Air Pollution
[Show abstract][Hide abstract] ABSTRACT: Retrievals of tropospheric nitrogen dioxide (NO2) from the Ozone Monitoring Instrument (OMI) are subject to errors in the treatments of aerosols, surface reflectance anisotropy, and vertical profile of NO2. Here we quantify the influences over China via an improved retrieval process. We explicitly account for aerosol optical effects (simulated by nested GEOS-Chem at 0.667 long. × 0.5 lat. and constrained by aerosol measurements), surface reflectance anisotropy, and high-resolution vertical profiles of NO2 (simulated by GEOS-Chem). Prior to the NO2 retrieval, we derive the cloud information using consistent ancillary assumptions.
We compare our retrieval to the widely used DOMINO v2 product, using MAX-DOAS measurements at three urban/suburban sites in East China as reference and focusing the analysis on the 127 OMI pixels (in 30 days) closest to the MAX-DOAS sites. We find that our retrieval reduces the interference of aerosols on the retrieved cloud properties, thus enhancing the number of valid OMI pixels by about 25%. Compared to DOMINO v2, our retrieval better captures the day-to-day variability in MAX-DOAS NO2 data ( R 2 Combining double low line 0.96 versus 0.72), due to pixel-specific radiative transfer calculations rather than the use of a look-up table, explicit inclusion of aerosols, and consideration of surface reflectance anisotropy. Our retrieved NO2 columns are 54% of the MAX-DOAS data on average, reflecting the inevitable spatial inconsistency between the two types of measurement, errors in MAX-DOAS data, and uncertainties in our OMI retrieval related to aerosols and vertical profile of NO2.
Sensitivity tests show that excluding aerosol optical effects can either increase or decrease the retrieved NO2 for individual OMI pixels with an average increase by 14%. Excluding aerosols also complexly affects the retrievals of cloud fraction and particularly cloud pressure. Employing various surface albedo data sets slightly affects the retrieved NO2 on average (within 10%). The retrieved NO2 columns increase when the NO2 profiles are taken from MAX-DOAS retrievals (by 19% on average) or TM4 simulations (by 13%) instead of GEOS-Chem simulations. Our findings are also relevant to retrievals of other pollutants (e.g., sulfur dioxide, ormaldehyde, glyoxal) from UV-visible backscatter satellite instruments.
Full-text · Article · Jan 2014 · Atmospheric Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: We conducted long-term network observations using standardized Multi-Axis Differential optical absorption spectroscopy (MAX-DOAS) instruments in Russia and ASia (MADRAS) from 2007 onwards. At seven locations (Cape Hedo, Fukue, and Yokosuka in Japan, Hefei in China, Gwangju in Korea, and Tomsk and Zvenigorod in Russia) with different levels of pollution, we obtained 80 927 retrievals of tropospheric NO2 vertical column density (TropoNO2VCD) and aerosol optical depth (AOD). In the technique, the optimal estimation of the TropoNO2VCD and its profile was performed using aerosol information derived from O4 absorbances simultaneously observed at 460-490 nm. This large data set was used to analyze NO2 climatology systematically, including temporal variations from the seasonal to the diurnal scale. The results were compared with Ozone Monitoring Instrument (OMI) satellite observations and global model simulations. Two NO2 retrievals of OMI satellite data (NASA ver. 2.1 and Dutch OMI NO2 (DOMINO) ver. 2.0) generally showed close correlations with those derived from MAX-DOAS observations, but had low biases of ~50%. The bias was distinct when NO2 was abundantly present near the surface and when the AOD was high, suggesting that the aerosol shielding effect could be important, especially for clean sites where the difference could not be attributed to the spatial inhomogeneity. Except for constant biases, the satellite observations showed nearly perfect seasonal agreement with MAX-DOAS observations, suggesting that the analysis of seasonal features of the satellite data were robust. The prevailing seasonal patterns with a wintertime maximum implied the dominance of anthropogenic emissions around our sites. The presence of weekend reductions at Yokosuka and Gwangju suggested the dominance of emissions from diesel vehicles, with significant weekly cycles, whereas the absence of such a reduction at Hefei suggested the importance of other sources. A global chemical transport model, MIROC-ESM-CHEM, was validated for the first time with respect to background NO2 column densities during summer at Cape Hedo and Fukue in the clean marine atmosphere.
Full-text · Article · Dec 2013 · Atmospheric Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: We conducted an intensive field campaign at the summit of Mt. Tai (1534
m a.s.l.), Shandong Province, located at the center of Central East
China, during the period 28 May to 30 June 2006, to study seasonal
maxima of regional air pollution with respect to ozone (O3)
and aerosols. The specific objectives, campaign design, and major
findings are summarized. High concentrations of O3 and its
precursors, and aerosols, were detected and studied in the context of
annual variations. Most importantly, we identified that emissions from
regional-scale open crop residue burning after the harvesting of winter
wheat, together with photochemical aging, strongly increased the
concentrations of O3, aerosols, and primary species relevant
to air quality in this month of the year. Studies of in-situ
photochemical activity, regional source attribution of O3,
O3-aerosol interactions, validation of satellite observations
of tropospheric NO2, behaviors of volatile organic compounds,
organic/inorganic aerosol species, loss rates of black carbon (BC), and
instrument inter-comparisons are also summarized. The observed BC levels
must have a strong impact on the regional climate.
Full-text · Article · Aug 2013 · Atmospheric Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: Despite the importance of the role of nitrogen dioxide (NO2)
in tropospheric chemistry, the causes leading to the discrepancy between
satellite-derived and modeled tropospheric NO2 vertical
column densities (VCDs) over East Asia remain unclear. Here the
reproducibility of satellite tropospheric NO2 VCD data by a
regional chemical transport model (CMAQ) with the Regional Emission
inventory in ASia (REAS) Version 2 is evaluated from the viewpoint of
the diurnal variation of tropospheric NO2 VCDs, where
satellite observations at different local times (SCIAMACHY/ENVISAT,
OMI/Aura, and GOME-2/Metop-A) are utilized considering literature
validation results. As a case study, we concentrate on June and December
2007 for a detailed evaluation based on various sensitivity simulations,
for example with different spatial resolutions (80, 40, 20, and 10 km)
for CMAQ. For June, CMAQ generally reproduces absolute values of
satellite NO2 VCDs and their diurnal variations over all 12
selected diagnostic regions in East Asia. In contrast, a difficulty
arises in interpreting the significant disagreement between satellite
and CMAQ values over most of the diagnostic regions in December. The
disagreement cannot be explained by any of the sensitivity simulations
performed in this study. To address this, more investigations, including
further efforts for satellite validations in wintertime, are needed.
Full-text · Article · May 2013 · Atmospheric Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: Gaseous and particulate semi-volatile carbonyl compounds were determined
every three hours in the atmosphere of Mount Tai (elevation, 1534 m) in
the North China Plain during 2-5, 23-24 and 25 June 2006 under clear sky
conditions. Using a two-step filter cartridge in a series, particulate
carbonyls were first collected on a quartz filter and then gaseous
carbonyls were collected on a quartz filter impregnated with
O-benzylhydroxylamine (BHA). After the two-step derivatization with BHA
and N,O-Bis(trimethylsilyl)trifluoroacetamide (BSTFA), carbonyl
derivatives were measured using a gas chromatography. The gaseous
concentrations were obtained as follow: glycolaldehyde (range 0-826 ng
m-3, average 303 ng m-3), hydroxyacetone (0-579 ng
m-3, 126 ng m-3), glyoxal (46-1200 ng
m-3, 487 ng m-3), methylglyoxal (88-2690 ng
m-3, 967 ng m-3), n-nonanal (0-500 ng
m-3, 89 ng m-3), and n-decanal (0-230 ng
m-3, 39 ng m-3). These concentrations are among
the highest ever reported in the urban and forest atmosphere. We found
that gaseous α-dicarbonyls (glyoxal and methylglyoxal) are more
than 20 times more abundant than particulate carbonyls and that
glycolaldehyde is one order of magnitude more abundant than in aerosol
phase. In contrast, hydroxyacetone and normal aldehydes (nonanal and
decanal) are equally present in both phases. Time-resolved variations of
carbonyls did not show any a clear diurnal pattern, except for
hydroxyacetone. We found that glyoxal, methylglyoxal and glycolaldehyde
positively correlated with levoglucosan (a tracer of biomass burning),
suggesting that a contribution from field burning of agricultural wastes
(wheat crops) is significant for the bifunctional carbonyls in the
atmosphere of Mt. Tai. Upward transport of the pollutants to the
mountaintop from the low lands in the North China Plain is a major
process to control the distributions of carbonyls in the upper
atmosphere over Mt. Tai.
Full-text · Article · May 2013 · ATMOSPHERIC CHEMISTRY AND PHYSICS